5 speed or automatic? if automatic that is pretty good for the winter!
5 speed that pretty good for the winter. mileage drops off in the winter because there is more moisture in the air and the fuel does not burn as efficiently and with colder air the combustion mixture is more lean anyway. also your engine takes longer to warm up to operating temperature where it is more efficient.
And there's the gasoline blends that they use in the winter time, I usually see a 5 mpg drop in economy when they switch over.